1. Field of the Invention
This invention relates generally to rotary mechanical end face seals and more particularly to rotary mechanical end face seals having spiral grooves for creating a fluid gap between the sealing faces.
2. Background Art
Mechanical face seals long have been used for sealing between a housing and a relatively rotating shaft. More recently, grooves have been introduced into the sealing face of at least one of the sealing rings to help generate a gap between the seal faces, which gap separates the rings. These type of seals are generally referred to as non-contacting seals. Spiral grooves have been utilized for pumping fluid between the seal faces so that the fluid creates a small gap between the faces during shaft rotation. Examples of spiral grooved faces are found in U.S. Pat. No. 3,499,653 and in No. 4,212,475, both of which are commonly assigned with the present invention and the teachings thereof which are incorporated herein by reference.
The spiral grooves heretofore disclosed comprise two generally smooth boundary curves which separate the grooved area from the land. These two boundary curves are essentially parallel to each other and each terminate at end points disposed essentially at the same radial distance from the centerline of the seal face. These two end points are joined by a transverse boundary which, for the most part, extends in the circumferential direction to produce the spiral groove patterns shown in FIG. 2 of each of U.S. Pat. Nos. 3,499,653 and 4,212,475.
It has been found that spiral grooves of the prior art seals are effective for providing a gap between the seal faces. Nevertheless, these types of seal face patterns have characteristics that result from the shape of the grooves. The shape of the grooves includes a single terminal corner at the point where the trailing boundary of the groove intersects a circumferential boundary of the groove to provide an acute angle at the intersection point. The angle is located between the two circumferential edges of the sealing face and is referred to herein as a terminal corner.
The single terminal corner design results in a pressure "zone" that is created adjacent the terminal corner of each groove. For the set of grooves in a standard spiral groove seal face, one such zone is produced by each groove. It is thought that this pressure zone occurs at a spot on the land immediately adjacent the groove terminal corner, and more specifically, at the edge of the land opposite the direction in which the seal face is relatively rotating and on the other side of the boundary line between the groove and land from the groove. The pressure buildup at this point is thought to occur because of the converging fluid mass flow into the terminal corner which occurs from the converging trailing and circumferential boundaries of the groove at the intersection point. In the conventional spiral groove sealing face, the pressure zones associated with each groove are thus each disposed at approximately the same radial position relative to the shaft centerline but are circumferentially displaced at or immediately adjacent the boundary line between the grooved portion and the ungrooved portion or dam.
The creation of a limited number of pressure zones, necessarily limited by the one-to-one relationship with each of the standard spiral grooves, is sufficient to provide enough lift to separate the faces of a mechanical face seal and to create the gap therebetween. In the spiral grooves of U.S. Pat. No. 3,499,653 and of No. 4,212,475, the number of pressure zones are limited to the total number of spiral grooves which are present in the seal face, and these are arranged at essentially identical radii along a circumferential line approximately adjacent the boundary between the grooved portion and the dam.